Turbine interstage seal assembly

ABSTRACT

Interstage leakage around the inner shrouds of the stationary vanes of a turbine is reduced by a seal assembly disposed in a space between turbine rotor wheels or discs. The members of the seal assembly are separated from the hot stator vanes and are supported by a seal housing cooled by air supplied through the hollow stator vanes. Thus, clearance between stationary members of the seal assembly and the rotor can be made smaller than in prior structures which had to allow for expansion of the members.

1451 Mar. 7, 1972 mompai aai.......................

[54} TURBINE INTERSTAGE SEAL ASSEMBLY 2,915,276 ii /i559 2,741,455 4/1956 Hunter.................

[72] inventors: Horace Wootton, Surf City, N.J.; George primary Emmine, Hem-y Raduazo Mlerley, wllmmgmni Attorney-A. r. Stratton, F. P. Lyle and F. Cristiano, Jr.

[57] ABSTRACT lnterstage leakage around the inner shrouds of the stationary [73] Assignee: Westinghouse Electric Corporation, Pittsburgh, Pa.

[22] Filed: Apr. 23, 1970 vanes of a turbine is reduced by a seal assembly disposed in a space between turbine rotor wheels or discs. The members of the seal assembly are separated from the hot stator vanes and [21] Appl.N0.: 31,120

415/113, 415/171 are supported by a seal housing cooled by air supplied through "WWFOM 11/00, o 11/10 the hollow stator vanes. Thus, clearance between stationary FieldofSearch..................415/109,110,111,115,170, members of the Seal assembly and the rotor can be made 415/171 175 17 113; 277/193 199 smaller than in prior structures which had to allow for expansion of the members.

[52] US. [51] Int.

5 Claims, 3 Drawing Figures [56] References Cited UNITED STATES PATENTS 3 ,529,904 9/197!) Scalz o et ,Ai ELUPWWVW PATENTEDHAR 7 I972 3,647. 31 1 sum 1 [IF 2 PATENTEDMAR 7 I972 SHEET 2 [IF 2 TURBINE INTERSTAGE SEAL ASSEMBLY BACKGROUND OF THE INVENTION This invention relates, generally, to elastic fluid machines and, more particularly, to interstage seals for axial flow gas turbines.

In order to improve the perfonnance of a multistage axial flow gas turbine it is desirable to control leakage between stages of the turbine. In prior turbines the clearances at certain points are necessarily large because the stationary members which control the clearances are integral with the stator vane segments and expand inwardly toward the rotor as the turbine comes up to operating temperature. Therefore, there is considerable leakage of the motive fluid past the stationary vanes of the turbine.

Furthermore, the operating temperatures of gas turbines are being increased to increase their output. The increase in operating temperature without exceeding the permissible temperature of the materials is attained by the introduction of a cooling fluid, such as air, into the turbine hot components such as the rotor blades and blade roots, and the stationary vane structure. It is desirable to conserve the cooling air and to direct its flow toward the hottest components of the turbine. Also, it is desirable to decrease the cost of a turbine by simplifying its structure.

SUMMARY OF THE INVENTION In accordance with one embodiment of the invention, clearances between stationary members of a turbine interstage seal assembly and points on the turbine rotor are reduced by utilizing radially disposed layers of thin sheet metal segments which cooperate with an annular seal housing member encircling the rotor to define an annular chamber between the rotor and the stator vane inner shroud segments. The sheet metal segments are separated from the hot vanes and are supported by the housing member which is cooled by air supplied through the hollow stator vanes. The pressure in the chamber is maintained at a value slightly higher than the pressure ahead of the stage so that there will be a positive flow of relatively cool air through relatively narrow passages between the seal members and the rotor. Part of the air is directed toward the roots of the rotor blades. The metal segments are attached to the housing member by means of bolts and spacers and the housing member is held concentric with the rotor axis by means of radial keys on the lower half of the housing member. The keys are adjustable in radial slots in the shroud segments by means of eccentric bushings on certain of the bolts which attach the metal segments to the housing member.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the nature of the invention, reference may be had to the following detailed description, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a view, in axial section, taken along the line II in FIG. 2, of a portion of an axial flow gas turbine having an interstage seal assembly constructed in accordance with principles of the invention;

FIG. 2 is a reduced view, partly in elevation and partly in section, taken along the line lI-II in FIG. 1, and

FIG. 3 is a detail view, in section, showing the key arrangement for holding the seal housing member concentric with the rotor axis.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, particularly to FIG. 1, the structure shown therein comprises a portion of an axial flow gas turbine which includes an annular array of circumferentially spaced stationary blades or vanes 11 secured between arcuate outer shroud segments (not shown) and arcuate inner shroud segments 13. The outer shroud segments are mounted in a stator blade ring (not shown) disposed inside a turbine casing (not shown) which is generally circular in cross section.

An annular row of rotor blades 14 is disposed immediately downstream from the stationary blades 11. The rotor blades are suitably attached to the periphery of a rotor wheel 15 secured to a shaft having an axis 16 and rotatably mounted in the turbine casing. The stationary blades 11 and the rotor blades 14 constitute one stage of the turbine which may include other stationary and rotary blades similar to the ones shown, thereby providing a multistage turbine.

A hot motive gas is supplied to the turbine from suitable combustion chambers (not shown). The hot motive gas flows from the combustion chambers into the turbine through a suitable transition passageway (not shown) and then through the stationary vanes and the rotor blades of the stages of the turbine. The rotor 15 is driven by energy extracted from the hot elastic fluid in a manner well known in the art.

Compressed coolant fluid may be introduced into the turbine through the stationary vanes 11, which are of a hollow construction and thence through an opening 17 in the shroud segment 13. The coolant fluid, such as air, may be supplied from a suitable source such as a compressor (not shown).

In order to conserve the coolant fluid and also to minimize leakage of the hot motive fluid around the stationary vanes 11, a seal assembly 21 is provided in the space between rotor wheels or discs 15 of the turbine. The seal assembly 21 is so constructed that it defines a substantially enclosed annular chamber 22 between the rotor 15 and the stator vane inner shroud segments 13 for receiving the coolant fluid. The pres sure of the coolant fluid inside the chamber 22 is maintained at a value slightly higher than the pressure of the motive fluid immediately upstream from the stationary vanes 11. Thus, the hot motive fluid is prevented from entering the chamber 22 and leakage of the hot motive fluid around the stationary vanes 11 is minimized.

In prior turbines, the clearance at points A and B has necessarily been large because the stationary members which control this clearance have been integral with the vane segments and expand inwardly toward the rotor as the turbine comes up to operating temperature. In the present structure, the clearance at points A and B can be much smaller because the members of the seal assembly 21 are separated from the hot vanes 11 and are supported by a seal housing member 23 which is cooled by the coolant fluid.

The annular seal housing member 23 has an axially extending portion 24 disposed in sealing relation with the rotor 15 and a radially extending flange 25 disposed in sealing relation with an inwardly extending projection 26 on the shroud segment 13. The projection 26 has a seal face 27 engaged by a seal face 28 on the flange 25. A labyrinth seal 29 may be provided between the portion 24 of the housing member 23 and the rotor 15.

Radially disposed relatively thin sheet metal segments 31 cooperate with the seal housing member 23 to define the substantially enclosed chamber 22 and to form a barrier to reduce loss of cooling air from the chamber. As shown, the segments 31 engage a seal surface 32 on the inner shroud segment 13 and the segments 31 are spaced a relatively small distance from an annular surface 33 on the rotor 15 to restrict the flow of cooling air through the annular passage at B. The segments 31 are disposed in two layers with expansion joints between segments staggered to prevent leakage between the ends of the segments. The gaps between the ends of the segments permit circumferential expansion of the segments due to rise in temperature.

Additional thin sheet metal segments 34 are disposed to engage a seal face 35 on the seal housing member 23 and a seal face 36 on the projection 26 on the shroud segment 13. As shown in FIG. 2, the segments 34 are disposed in two layers with expansion joints between layers staggered in the same manner as the segments 31. The segments 34 have an axially extending portion 37 spaced from a projection 38 on the rotor wheel 15 to maintain a relatively small clearance at point A.

Thus, the flow of coolant fluid which leaks through the labyrinth seal 29 into the space 39 is restricted at point A. In this manner coolant fluid is directed through an opening 41 in a sideplate 42 on the rotor wheel to cool the root portions of the rotor blades 14 in a manner fully described in a copending application Ser. No. 739,274, filed June 24, 1968 by A. J. Scalzo and Andrew Zabrodsky and assigned to the Westinghouse Electric Corporation. The seal segments 34 also cooperate with the seal housing member 23 to prevent loss of cooling air from the chamber 22 at the seal surfaces 27 and 28.

As shown more clearly in FIGS. 1 and 2, the seal segments 31 and 34 are attached to the flange 25 by two bolts 43 per segment. The segments 31 are spaced from the flange 25 by pipe spacing members 44 which engage a shoulder 45 at the head of each bolt. Resilient means, such as a Belleville spring washer 46, is disposed around the shoulder 45 between the end of the pipe spacer 44 and the segments 31 to control the clamping action on the metal segments 31. In this manner the loading on the segments is limited so that the segments can slide under the boltheads without danger of buckling.

The seal segments 34 are spaced from the flange 25 by means of pipe spacers 47 disposed between the flange 25 and a shoulder 48 on a nut 49 threaded onto each bolt 43. A Belleville washer 46 is disposed around the shoulder 48 to control the pressure applied on the segments 34 in the manner hereinbefore described. As shown more clearly in FIG. 2, elongated holes 51 are provided in the segments 34 for the bolts 43 to allow for circumferential growth while retaining positive positioning of the segments in a radial direction. Likewise, elongated holes 51 are provided in the segments 31 for the bolts 43.

As shown more clearly in FIGS. 2 and 3, the seal housing member 23 is held concentric with the rotor axis 16 by means of 6 radial keys 52 disposed in radial slots 53 in the projections 26 on the shroud segments 13. The keys 52 are provided in the lower half only of the seal housing member 23. The keys 52 are adjustable by means of eccentric bushings 54 on the bolts 43, thereby assuring proper alignment of the seal housing member 23. The keys 52 and eccentric bushings 54 take the place of the pipe spacers 47 on the bolts on which the keys are mounted. In this manner the seal segments 34 are maintained in spaced relation with the seal housing member 25, and the desired pressure on the seal segments is maintained. As previously stated, the keys 52 are provided in only the lower half of the seal housing member 23 and the key may be spaced in the manner shown in FIG. 2. The bolts 43 and pipe spacers 47 are provided between the keys 52 in the lower half of the seal housing member 23.

Another feature of the present seal arrangement is that the flexible nature of the seal segment plates 31 permits an initial cold spring pressure between surfaces at 32, thereby assuring that the joint between the seal segments 31 and the shroud segment 13 stays tight. As previously explained, the segments 34 cooperate with the seal housing member 23 and the shroud segment 13 to prevent leakage of the cooling air through the joint between seal surfaces 27 and 28.

From the foregoing description it is apparent that the invention provides a seal assembly which makes it possible to reduce clearances between stationary and rotating parts of a turbine since the members of the seal assembly are separated from hot portions of the turbine and they are supported on a member which is cooled by cooling air introduced into the turbine. The seal assembly conserves the cooling air and directs its flow in a manner to cool otherwise hot portions of the turbine. Furthermore, the seal assembly minimizes leakage of the hot motive fluid around the stationary vanes of the turbine.

We claim as our invention:

1. In a seal assembly for an axial flow machine utilizing a hot pressurized motive fluid,

a stator having an annular array of stator vanes with inner shroud segments secured to the vanes,

a rotor having an annular row of rotor blades disposed downstream from the stator vanes, an annular seal housing member enclrclrng the rotor up stream from the rotor blades,

radially disposed metal segments cooperating with the housing member to define a substantially enclosed annular chamber between the rotor and the stator vane inner shroud segments to prevent leakage of the motive fluid around the stator vanes,

said housing member having an axially extending portion disposed in sealing relation with said rotor and a radially extending flange disposed in sealing relation with said inner shroud segments, and

means for attaching said metal segments to the radially extending flange on said housing member in axially spaced relation.

2. The seal assembly defined in claim 1, wherein the attaching means includes bolts extending through said flange and spacing members disposed between the metal segments and the flange to apply a clamping action on the segments.

3. The seal assembly defined in claim 2, wherein the metal segments are disposed in layers with staggered expansion joints between segments.

4. The seal assembly defined in claim 3, including resilient means for controlling the clamping action on the metal segments.

5. The seal assembly defined in claim 2, including inwardly extending projections on the shroud segments having radial slots therein, radial keys on the lower half of the housing member and disposed in certain of said slots for holding the housing member concentric with the rotor axis, and eccentric bushings on certain of said bolts for adjusting said keys in said slots. 

1. In a seal assembly for an axial flow machine utilizing a hot pressurized motive fluid, a stator having an annular array of stator vanes with inner shroud segments secured to the vanes, a rotor having an annular row of rotor blades disposed downstream from the stator vanes, an annular seal housing member encircling the rotor upstream from the rotor blades, radially disposed metal segments cooperating with the housing member to define a substantially enclosed annular chamber between the rotor and the stator vane inner shroud segments to prevent leakage of the motive fluid around the stator vanes, said housing member having an axially extending portion disposed in sealing relation with said rotor and a radially extending flange disposed in sealing relation with said inner shroud segments, and means for attaching said metal segments to the radially extending flange on said housing member in axially spaced relation.
 2. The seal assembly defined in claim 1, wherein the attaching means includes bolts extending through said flange and spacing members disposed between the metal segments and the flange to apply a clamping action on the segments.
 3. The seal assembly defined in claim 2, wherein the metal segments are disposed in layers with staggered expansion joints between segments.
 4. The seal assembly defined in claim 3, including resilient means for controlling the clamping action on the metal segments.
 5. The seal assembly defined in claim 2, including inwardly extending projections on the shroud segments having radial slots therein, radial keys on the lower half of the housing member and disposed in certain of said slots for holding the housing member concentric with the rotor axis, and eccentric bushings on certain of said bolts for adjusting said keys in said slots. 